1. Field of the Invention
The present invention relates to two-side video discs and a method of manufacturing the same, and more particularly, to a video disc having high definition television (HDTV) video signals recorded on both sides and a method of manufacturing such a two-side video disc.
2. Description of the Background Art
Conventionally, a band-division method is used as a method for recording a HDTV video signal having a broad band on a disc record without rotating the same at a special high speed.
When a conventional HDTV signal is recorded by such band-division method, a HDTV video signal of each line is first divided into signals of two channels and then a period of each line is expanded twice as long. Then, a luminance signal component and a line sequential color difference component are time-divisionally multiplexed on each line to form video signals of two channels, so that a recording band of the video signal of each channel is reduced by half.
Two recording laser beams emitted in close proximity are modulated separately by these video signals of narrow record band to form double spiral recording tracks on one side face of the video disc. Because such a recording method divides a HDTV video signal into two channels, the recording band of each channel, i.e. of each recording track on the disc, is a half of that of the HDTV video signal.
When reproducing a HDTV video signal from a video disc having the recording tracks formed in the above described manner, the recorded signals of two channels are separately read from the double spiral recording tracks by two reproduction laser beams emitted in close proximity. The read out signals of the two channels are combined to form the original HDTV video signal.
According to the conventional recording/reproduction method of such a video disc, the record band of each recording track is a half of that of the original HDTV video signal. The rotating speed of the disc at the time of reproduction can be made a half of that of reproducing a HDTV video signal that is recorded without being divided into two channels.
However, the above described conventional example had a disadvantage that video reproduction of a long time period is difficult because the reproduction time period is 1/2 due to two recording tracks formed on the surface of the disc in comparison with the case wherein only a single recording track is formed.
Furthermore, the above described conventional example had the possibility of the reproduction signals of the two channels from these recording tracks being missing at the same time by dropouts because video signals of two channels are simultaneously recorded on two adjacent recording tracks. It was necessary to subject the signal to be recorded to interleave processing for each recording track to prevent an image from completely being missing in case of occurrence of such dropouts at the proximate lines of the HDTV signal, which led to extremely complicated recording and reproduction circuits.
Japanese Patent Laying-Open No. 61-21424 discloses a stereoscopic video disc where one spiral recording track is formed on the top side face and another is formed on the back side face, in opposite directions, on a video disc. At the time of reproduction, signals are reproduced simultaneously from the two recording tracks on the top and back side faces. According to this background art, it is not necessary to consider the tolerance of the timing of reproduction since two kinds of reproduced signals form respective pictures separately. In addition, this background art does not refer to the recording and reproduction of a HDTV video signal.